1. Field of the Invention
This invention relates to computer memories, and more specifically for a memory to self-identify its access time.
2. Prior Art
The use of various memory devices for storing information is well-known in the prior art. These memory devices can be internal or external devices and are coupled to a host unit, such as a central processing unit (CPU). The host unit provides the addressing, as well as other control signals, to access a location in memory for reading or writing information to and from such a location.
Although various memory units can be configured with a given host hardware, the memory unit must be configured to function with a particular host unit. At the time a particular memory unit is configured within the system, the host unit must be capable of operating with the memory unit. Proper hand shaking and synchronization are essential elements for information transfer to be established between the two units. In a typical situation, the memory unit is configured to a previously determined host unit, such as a CPU, so that the memory unit must be specially designed to operate within certain limited constraints imposed by the host unit.
Because different memory units operate at different speeds, each memory unit must be specially configured and interfaced to operate with a given CPU. Such interfacing must be accomplished at the time the memory unit is coupled to the CPU, or typically, the memory unit is predesigned to operate at a given speed determined by the CPU.
Where a number of memory units are coupled to the same CPU, a further problem is encountered in that some of the memory units may operate at different speeds. Because random-access memories (RAM) are capable of running at a faster speed than read-only memories (ROM), the CPU must know the location or address of these various memory units so that the host unit can change its accessing speed if efficient use of these memories is desired. If the CPU cannot differentiate among the different memories, then it must operate at the accessing speed of the slowest memory unit.
In another related technology, modularized memory units are being designed for various uses. In one area, memory modules are designed to be plugged into various interfacing connectors, such that various modules representing different memory types are interfaced with the same host unit. In the prior art a given memory type must be plugged into a predesigned location, so that the CPU knows the characteristics of the memory unit by its location. However, such, a preordained system limits the flexibility of modularized design. What is desired in this instance is to have a memory unit having a capability of being plugged into any given module location and permitting the CPU to identify that memory unit by its type and not by the location that it is plugged into.
In another application, a memory connection is coupled to a host unit. However, the memory connection is capable of interfacing with various types of memory units. For example, in an automatic bank teller machine, or a security/identification machine, a memory unit, such as a bankcard having a magnetic strip, is inserted into the connection for accessing the host unit. Although the bank teller machines of today read magnetic strips on cards, a more sophisticated unit can access memory devices which contain substantial memory mass storage. Compact and portable mass storage units are achieved by utilizing integrated circuit semiconductor memories. In the above example, the host unit must be capable of identifying the different types of memory units which plug into the machine and for efficient operation the machine must be capable of accessing these various memory units at accessing speeds which correspond to the different memory units.
Therefore, in implementing modularized memory designs, it is appreciated that what is needed is a self-identifying memory, wherein a particular memory unit provides certain identifying information for its access by the host unit. One such information being its memory accessing speed.